Phase change material, a phase change random access memory device including the phase change material, a semiconductor structure including the phase change material, and methods of forming the phase change material

ABSTRACT

A phase change material including a high adhesion phase change material formed on a dielectric material and a low adhesion phase change material formed on the high adhesion phase change material. The high adhesion phase change material includes a greater amount of at least one of nitrogen and oxygen than the low adhesion phase change material. The phase change material is produced by forming a first chalcogenide compound material including an amount of at least one of nitrogen and oxygen on the dielectric material and forming a second chalcogenide compound including a lower percentage of at least one of nitrogen and oxygen on the first chalcogenide compound material. A phase change random access memory device, and a semiconductor structure are also disclosed.

TECHNICAL FIELD

Embodiments of the present invention relate to a phase change materialhaving improved adhesion to a dielectric material. More specifically,the present invention, in various embodiments, relates to a phase changematerial including at least two portions, one portion having a higherpercentage of at least one of nitrogen and oxygen than the otherportion, methods of producing the phase change material, and devicesincorporating the phase change material.

BACKGROUND

Phase change materials are known in the art and include compounds formedfrom germanium (Ge), antimony (Sb), and tellurium (Te), which are knownas GST materials. The phase change material is capable of beingreversibly electrically switched between an amorphous state and acrystalline state. The phase change material is electrically writableand erasable and has been used in electronic memory applications. Whenthe phase change material is in the amorphous state, it is said to be“reset,” while the phase change material is said to be “set” in thecrystalline state. Phase change materials have been used in phase changerandom access memory (“PCRAM”) devices to provide non-volatile memorywith long data retention. PCRAM devices rely on the electricallybistable status of resistance differences between the amorphous andcrystalline states of the phase change material.

One GST material conventionally used in PCRAM devices is Ge₂Sb₂Te₅.However, during fabrication of the PCRAM device, the GST materialexhibits a low adhesion to a dielectric material upon which the GSTmaterial is formed. The dielectric material includes silicon oxide(SiO_(x)) or silicon nitride (SiN_(x)). In other words, the GSTmaterial, as deposited on the dielectric material, tends to delaminateor peel away from the dielectric material during the fabricationprocess. It would be desirable to form a phase change material havingimproved adhesion to the dielectric material in devices utilizing phasechange materials.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a memory cell including a phasechange material formed in accordance with an embodiment of theinvention;

FIG. 2 is a cross-sectional view illustrating the fabrication of a PCRAMdevice in accordance with an embodiment of the invention; and

FIG. 3 is a deposition system in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION

A phase change material having improved adhesion to a dielectricmaterial and methods of forming such a phase change material aredisclosed. As used herein, the phrase “phase change material” means andincludes a chalcogenide compound formed from a chalcogen ion and atleast one electropositive element. The phase change material includes atleast two portions, with one of the portions having an increased contentof at least one of nitrogen and oxygen relative to the other portion.Increasing the amount of nitrogen or oxygen in a first portion of thephase change material provides improved adhesion between the phasechange material and the underlying dielectric material. Accordingly, aphase change material having the desired adhesion to the dielectricmaterial is produced.

The following description provides specific details, such as materialtypes, material thicknesses, and processing conditions in order toprovide a thorough description of embodiments of the present invention.However, a person of ordinary skill in the art will understand that theembodiments of the present invention may be practiced without employingthese specific details. Indeed, the embodiments of the present inventionmay be practiced in conjunction with conventional fabrication techniquesemployed in the industry. In addition, the description provided hereindoes not form a complete process flow for manufacturing a PCRAM device,and the PCRAM device described below does not form a completesemiconductor device. Only those process acts and structures necessaryto understand the embodiments of the present invention are described indetail below. Additional acts to form a complete semiconductor deviceincluding the PCRAM device may be performed by conventional techniques.

The materials described herein may be formed by any suitable techniqueincluding, but not limited to, spin coating, blanket coating, chemicalvapor deposition (“CVD”), atomic layer deposition (“ALD”), plasmaenhanced ALD, or physical vapor deposition (“PVD”). Alternatively, thematerials may be grown in situ. Depending on the specific material to beformed, the technique for depositing or growing the material may beselected by a person of ordinary skill in the art. While the materialsdescribed and illustrated herein may be formed as layers, the materialsare not limited thereto and may be formed in other three-dimensionalconfigurations.

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shown,by way of illustration, specific embodiments in which the invention maybe practiced. These embodiments are described in sufficient detail toenable a person of ordinary skill in the art to practice the invention.However, other embodiments may be utilized, and structural, logical, andelectrical changes may be made without departing from the scope of theinvention. The illustrations presented herein are not meant to be actualviews of any particular system, phase change material, or PCRAM device,but are merely idealized representations which are employed to describethe present invention. The drawings presented herein are not necessarilydrawn to scale. Additionally, elements common between drawings mayretain the same numerical designation.

The chalcogen ion of the phase change material may be oxygen (O), sulfur(S), selenium (Se), Te, or polonium (Po). In one embodiment, thechalcogen ion is Te. The electropositive element may include, but is notlimited to, nitrogen (N), silicon (Si), nickel (Ni), gallium (Ga), Ge,arsenic (As), silver (Ag), indium (In), tin (Sn), Sb, gold (Au), lead(Pb), bismuth (Bi), or combinations thereof. In one embodiment, theelectropositive elements are Ge and Sb. The chalcogenide compound may bea binary, ternary, or quaternary alloy of these elements. By way ofnon-limiting example, the chalcogenide compound may be a compound of Ge,Sb, and Te (a GST material). The GST material may have an empiricalformula of Ge_(x)Sb_(100-(x+y))Te_(y), where the stoichiometry (inatomic percent) of Ge and Te are indicated by x and y, respectively, andthe remainder of the GST material is Sb. By way of non-limiting example,x may be greater than approximately 5 atomic percent but less thanapproximately 60 atomic percent, such as between approximately 17 atomicpercent and approximately 44 atomic percent, and y may be greater thanapproximately 20 atomic percent but less than approximately 70 atomicpercent, such as between approximately 23 atomic percent andapproximately 56 atomic percent. By way of non-limiting example, the GSTmaterial may be Ge₂₂Sb₂₂Te₅₅ (also known as Ge₂Sb₂Te₅), Ge₈Sb₃₂Te₅₆(also known as Ge₁Sb₄Te₇), Ge₁₄Sb₂₈Te₅₆ (also known as Ge₁Sb₂Te₄),Ge₄₀Sb₉Te₅₁, Ge₄₄Sb₅Te₅₁, Ge₂₈Sb₂₇Te_(45,) Ge₅₈Sb₁₉Te₂₃, Ge₁₇Sb₂₇Te₅₆,Ge₃₀Sb₁₇Te₅₃, or combinations thereof. While compounds having specificstoichiometries are listed above, the phase change material may includeother stoichiometries of Ge, Sb, and Te.

While specific examples herein describe the phase change material as aGST material, the phase change material may be a chalcogenide compoundformed from combinations of the other elements described above. By wayof non-limiting example, the chalcogenide compound may be a compound ofSb and Te, such as Sb₂Te₃, a compound of Ge and Te, such as GeTe, acompound of In and Se, such as In2Se₃, a compound of Sn and Te, such asSnTe, a compound of Bi and Te, such as Bi₂Te₃, a compound of Sb and Te,such as SbTe, a compound of Sn and Se, such as SnSe, a compound of Geand Se, such as GeSe, a compound of Au, Ge, Sn, and Te, such asAu₂₅Ge₄Sn₁₁Te₆₀, a compound of Ag and Se, such as Ag₂Se, or a compoundof In and Te, such as InTe. While chalcogenide compounds having specificstoichiometries are listed above, the chalcogenide compound may includethe same combination of elements having other stoichiometries.

FIG. 1 is an illustration of a memory cell 100 including a phase changematerial 102. The memory cell 100 includes a substrate 101 upon whichthe phase change material 102 is formed. The phase change material 102may include at least two portions 108, 110 thereof. The substrate 101may include a conventional silicon substrate or other bulk substrateincluding a layer of semiconductor material. As used herein, the term“bulk substrate” includes not only silicon wafers, but alsosilicon-on-insulator (“SOI”) substrates, silicon-on-sapphire (“SOS”)substrates, epitaxial layers of silicon on a base semiconductorfoundation, and other semiconductor or optoelectronics materials, suchas silicon-germanium, germanium, gallium arsenide, or indium phosphide.The material of the substrate 101 may be doped or undoped. A dielectricmaterial 104 may be formed over the surface of the substrate 101. Thedielectric material 104 may be formed from a SiO_(x) or SiN_(x) materialsuitable as an insulative or dielectric material, such as, for example,SiO, SiO₂, or Si₃N₄. The dielectric material 104 may be formed byconventional techniques, such as by plasma enhanced CVD (“PECVD”) orstandard thermal CVD. The dielectric material 104 may be patterned, asknown in the art, to form apertures (not shown) therein. A lowerelectrode 106 may be formed within the apertures of the dielectricmaterial 104 by conventional techniques. The material used for the lowerelectrode 106 may be a conductive material, such as tungsten (W), nickel(Ni), tantalum nitride (TaN), platinum (Pt), tungsten nitride (WN), gold(Au), titanium nitride (TiN), or titanium aluminum nitride (TiAlN). Thephase change material 102 may be formed onto upper, exposed surfaces ofthe lower electrode 106 and the dielectric material 104, such as by PVD.

The phase change material 102 may be sufficiently adherent to thedielectric material 104 to form an operative memory cell 100. Otherwise,the phase change material 102 may delaminate from the dielectricmaterial 104, rendering the memory cell 100 inoperable for use in aPCRAM device. To provide increased adhesion of the phase change material102 to the dielectric material 104, nitrogen, oxygen, or a combinationthereof may be incorporated into a first portion 108 of the phase changematerial 102. As such, the first portion 108 of the phase changematerial 102 may have an increased amount of at least one of nitrogenand oxygen relative to a second portion 110 of the phase change material102. For convenience, the remainder of the application refers tonitrogen or oxygen being present in the first portion 108 of the phasechange material 102. However, it is understood that a combination ofnitrogen and oxygen may also be present.

The two portions 108, 110 of the phase change material 102 may be formedover the lower electrode 106 and the dielectric material 104. The firstportion 108 of phase change material 102, which is in contact with thelower electrode 106 and the dielectric material 104, may exhibitincreased adhesion to the dielectric material 104 and is also referredto herein as high adhesion phase change material 108. The high adhesionphase change material 108 may be formed in direct contact with the uppersurface of the dielectric material 104 and lower electrode 106. Thesecond portion 110 of the phase change material 102 may exhibit a lowerdegree of adhesion to the dielectric material 104 and is referred toherein as low adhesion phase change material 110. The low adhesion phasechange material 110 may be formed over and in contact with the highadhesion phase change material 108. The high adhesion phase changematerial 108 and low adhesion phase change material 110 are collectivelyreferred to herein as phase change material 102.

The high adhesion phase change material 108 may include a sufficientamount of nitrogen or oxygen such that a high degree of adhesion betweenthe high adhesion phase change material 108 and the dielectric material104 is achieved. By forming the low adhesion phase change material 110over the high adhesion phase change material 108 and not in directcontact with the dielectric material 104, the phase change material 102may have sufficient adherence to the dielectric material 104 to preventdelamination The strength of adhesion between the phase change material102 and the dielectric material 104 may be measured by the fractureenergy sufficient to cause an adhesion failure between the phase changematerial 102 and the dielectric material 104. The adhesion strength maybe determined in a four point bend test, as known in the art. A highstrength of adhesion corresponds to a high fracture energy sufficient tocause the adhesion failure, or delamination, of the phase changematerial 102 from the dielectric material 104. The high adhesion phasechange material 108 may provide a high adhesion strength between thephase change material 102 and the dielectric material 104. In oneembodiment, the fracture energy between the phase change material 102and the dielectric material 104 may be at least about 0.94 J/m², such asat least about 1.5 J/m². In another embodiment, the fracture energybetween the phase change material 102 and the dielectric material 104may be at least about 2.0 J/m².

In order to achieve a high adhesion strength, the high adhesion phasechange material 108 may include greater than or equal to about 5%(atomic) of nitrogen, oxygen, or a combination thereof. While increasingthe amount of nitrogen or oxygen in the high adhesion phase changematerial 108 may increase the degree of adhesion between the highadhesion phase change material 108 and the dielectric material 104, ifthe same amount of nitrogen or oxygen is present in the entire phasechange material 102, the ability of the phase change material 102 tocrystallize may be affected. Stated another way, if the phase changematerial 102 includes too much nitrogen or oxygen, the phase changematerial 102 may be unable to crystallize, which affects the ability ofthe phase change material 102 to electrically switch between theamorphous and crystalline states. As such, if the phase change material102 includes too high of an amount of nitrogen or oxygen, the phasechange material 102 may not be suitable for use in a PCRAM device. Toenable the phase change material 102 to crystallize, the increasednitrogen or oxygen content is present in the high adhesion phase changematerial 108 while the low adhesion phase change material 110 includesless or no nitrogen or oxygen. Since only a portion of the phase changematerial 102 includes a greater amount of nitrogen or oxygen, the phasechange material 102 may still be capable of electrically switching. Evenif the high adhesion phase change material 108 includes greater thanabout 10% (atomic) of nitrogen or oxygen, such as from about 10%(atomic) to about 20% (atomic) of nitrogen or oxygen, the phase changematerial 102 may be capable of electrically switching. In oneembodiment, to enable the phase change material 102 to crystallize, thehigh adhesion phase change material 108 may include less than or equalto about 8% (atomic) of nitrogen or oxygen. As such, to provide thedesired adhesion, the high adhesion phase change material 108 mayinclude from greater than or equal to about 5% (atomic) to less than orequal to about 8% (atomic) of nitrogen or oxygen. In another embodiment,the high adhesion phase change material 108 may include from about 6%(atomic) to about 7% (atomic) of nitrogen or oxygen.

The memory cell 100 may, optionally, include a high adhesion phasechange material 108′ formed over the low adhesion phase change material110, as illustrated in FIG. 1 with dashed lines. The high adhesion phasechange material 108′ may provide increased adhesion between an upperelectrode 120 (see FIG. 2) and the phase change material 102.

Relative to the high adhesion phase change material 108, the lowadhesion phase change material 110 may include a decreased amount ofnitrogen, oxygen, or a combination thereof. The decreased amount ofnitrogen or oxygen in the low adhesion phase change material 110 mayensure the phase change material 102 is capable of crystallizing,enabling adequate use thereof in a PCRAM device. By way of example only,the low adhesion phase change material 110 may include from about 0%(atomic) to less than about 5% (atomic) of nitrogen or oxygen, such asless than about 4% (atomic) of nitrogen or oxygen. In one embodiment,the low adhesion phase change material 110 may include about 2.5%(atomic) of nitrogen or oxygen.

The thickness of the high adhesion phase change material 108 and the lowadhesion phase change material 110 may depend on the size and shape ofthe memory cell 100 ultimately to be formed in the PCRAM device. Sincethe only portion of the phase change material 102 in contact with thedielectric material 104 is the high adhesion phase change material 108,improved adhesion between the dielectric material 104 and the phasechange material 102 may be achieved by providing a thin layer of thehigh adhesion phase change material 108 between the dielectric material104 and the low adhesion phase change material 110. For example, thehigh adhesion phase change material 108 may have a thickness rangingfrom about 10 Å to about 100 Å. The remainder of the phase changematerial 102 may include the low adhesion phase change material 110. Byway of non-limiting example, if the phase change material 102 is formedat a total thickness of about 1000 Å, the high adhesion phase changematerial 108 may account for about 50 Å of the phase change material 102and the low adhesion phase change material 110 may account for about 950Å of the phase change material 102.

Since the phase change material 102 includes two portions 108, 110, thephase change material 102 may have a substantially heterogeneouscomposition throughout its thickness. For example, the high adhesionphase change material 108 and low adhesion phase change material 110 maybe chalcogenide materials differing in their respective atomicpercentages of nitrogen or oxygen. The distinct materials or portions ofthe phase change material 102 may be distinguishable by visual orchemical means, such as by microscopy or chemical analysis. By way ofnon-limiting example, if the phase change material 102 were viewed bytransmission electron microscopy, the high adhesion phase changematerial 108 and low adhesion phase change material 110 may be visuallydistinguishable from one another. In addition, chemical analysis, suchas x-ray photoelectron spectroscopy (“XPS”) or inductively coupledplasma (“ICP”) spectrometry, may be used to distinguish the two portionsof the phase change material 102.

The phase change material 102 may be used in a PCRAM device 112, asillustrated in FIG. 2. While specific examples herein describe andillustrate the phase change material 102 in a PCRAM device 112, thephase change material 102 may also be used in a complementarymetal-oxide semiconductor (“CMOS”) device or in an optical disc, such asa DVD/RW. The PCRAM device 112 includes a memory matrix or array (notshown) that includes a plurality of memory cells 100 for storing data.The memory matrix is coupled to periphery circuitry (not shown) by aplurality of control lines. The periphery circuitry may includecircuitry for addressing the memory cells 100 contained within thememory matrix, along with circuitry for storing data in and retrievingdata from the memory cells 100. The periphery circuitry may also includeother circuitry used for controlling or otherwise ensuring the properfunctioning of the PCRAM device 112.

As shown in FIG. 2, the PCRAM device 112 includes substrate 101, digitline 114, n-doped polysilicon material 116, p-doped polysilicon material118, dielectric material 104, lower electrode 106, phase change material102 (high adhesion phase change material 108 and low adhesion phasechange material 110), upper electrode 120, insulative material 122,oxide material 124, and contact hole 126 filled with conductive material128. The PCRAM device 112 may be formed by conventional techniques,which are not described in detail herein. The PCRAM device 112 may,optionally, include the high adhesion phase change material 108′ (notillustrated in FIG. 2) formed between the low adhesion phase changematerial 110 and the upper electrode 120. The high adhesion phase changematerial 108′ may provide increased adhesion between the upper electrode120 and the phase change material 102.

To form the two portions of the phase change material 102 (the highadhesion phase change material 108 and low adhesion phase changematerial 110) on the dielectric material 104, the phase change material102 may be formed by a deposition technique in which a plasma is capableof being formed and in the presence of nitrogen gas, oxygen gas, or acombination thereof. The nitrogen gas or oxygen gas may be present in adeposition chamber as the high adhesion phase change material 108 isformed but may be absent as the low adhesion phase change material 110is formed. By way of non-limiting example, the deposition technique maybe a PVD technique or a CVD technique. PVD includes, but is not limitedto, sputtering, evaporation, or ionized PVD. Such deposition techniquesare known in the art and, therefore, are not described in detail herein.

A system 132 for forming the phase change material 102 on the dielectricmaterial 104 is illustrated in FIG. 3. The substrate 101 including thedielectric material 104 may be positioned or placed on a support orchuck (not shown) of a deposition chamber 134 in which a plasma 136 iscapable of being produced. The deposition chamber 134 may also beconfigured to introduce nitrogen gas or oxygen gas 138 therein. Byadjusting the flow rate of nitrogen gas or oxygen gas 138 into thedeposition chamber 134, the high adhesion phase change material 108 andthe low adhesion phase change material 110 may be formed. The plasma 136produced in the deposition chamber 134 may be an inert plasma producedfrom a noble gas element, such as a helium, neon, argon, krypton, xenon,or radon. In one embodiment, an argon plasma is generated. The nitrogengas or oxygen gas 138 may be introduced into the deposition chamber 134at a flow rate of from about 0 standard cubic centimeters per minute(“sccm”) to about 5 sccm. By way of non-limiting example, the depositionchamber 134 may be a conventional PVD chamber or PVD tool. Sinceconventional PVD chambers are capable of producing the plasma 136 and ofintroducing nitrogen gas or oxygen gas 138, a conventional PVD chambermay be used in the present invention without modification thereto. Inone embodiment, the deposition chamber is an Entron system, such as anEntron EX300 RF sputtering chamber, which is commercially available fromUlvac Technologies, Inc. (Methuen, Mass.).

The deposition chamber 134 may also include a deposition target 140formed from a chalcogenide material having the same, or substantiallysimilar, combination and stoichiometry of elements as those of the phasechange material 102 to be formed. The deposition target 140 may beselected by a person of ordinary skill in the art depending on the phasechange material 102 to be formed. By way of non-limiting example, thedeposition target 140 may be a Ge₂Sb₂Te₅ target, known as a 225 target,or a Ge₁Sb₄Te₇ target, known as a 147 target. Such deposition targets140 are commercially available, such as from Nikko Materials USA, Inc.(Chandler, Ariz.), MMC Technology, Inc. (San Jose, Calif.), and UmicoreGroup (Brussels, Belgium). In one embodiment, the deposition target 140is a 225 target.

After positioning the substrate 101 having the dielectric material 104on the chuck, the high adhesion phase change material 108 may be formedon the dielectric material 104. The plasma 136 may be generated in thedeposition chamber 134 and the nitrogen gas or oxygen gas 138 may beintroduced into the deposition chamber 134. Conditions, such astemperature and pressure, for generating and maintaining the plasma 136in the deposition chamber 134 may be conventional and, therefore, arenot described in detail herein. The flow rate of the nitrogen gas oroxygen gas 138 during formation of the high adhesion phase changematerial 108 may range from greater than about 1 sccm to about 5 sccm.As the deposition target 140 is bombarded with the plasma 136, atoms ofthe deposition target 140 are sputtered from the target surface anddeposited on the surface of the dielectric material 104. Nitrogen fromthe nitrogen gas or oxygen from the oxygen gas may covalently bond tothe deposited atoms, forming a coating of the high adhesion phase changematerial 108 on the surface of the dielectric material 104. The nitrogenor oxygen content of the high adhesion phase change material 108 maydepend on the flow rate of the nitrogen or oxygen gas 138. The greaterthe flow rate of the nitrogen or oxygen gas 138 into the depositionchamber 134, the greater the percentage of nitrogen or oxygenincorporated into the high adhesion phase change material 108. A desiredthickness of the high adhesion phase change material 108 may beachieved, as known in the art, by controlling the deposition time andthe power supplied to the deposition target. After the desired thicknessof the high adhesion phase change material 108 is produced, the flowrate of the nitrogen gas or oxygen gas 138 may be reduced to less thanabout 1 sccm to form the low adhesion phase change material 110. Sincethe nitrogen or oxygen introduced into the deposition chamber 134 duringthe formation of the low adhesion phase change material 110 issubstantially less, the low adhesion phase change material 110 mayinclude a low amount of nitrogen or oxygen or may be substantially freeof nitrogen or oxygen. In one embodiment, the flow rate of nitrogen gasor oxygen gas 138 may initially be about 5 sccm, forming a thin layer ofthe high adhesion phase change material 108 on the surface of thedielectric material 104. The high adhesion phase change material 108 mayhave a thickness of from about 10 Å to about 100 Å. The flow rate of thenitrogen gas or oxygen gas 138 may then be reduced to about 1 sccm,forming the low adhesion phase change material 110 over the highadhesion phase change material 108. The low adhesion phase changematerial 110 may be deposited until the phase change material 102reaches the desired thickness, such as for example, 1000 Å.

The two portions of the phase change material 102 may be formed in asingle deposition chamber 134 by adjusting the flow rate of the nitrogengas or oxygen gas 138 during deposition thereof. By forming both thehigh adhesion phase change material 108 and the low adhesion phasechange material 110 in sit, the phase change material 102 may beproduced using a single deposition act. As such, the phase changematerial 102 may be produced in a cost-effective manner. In addition,the throughput for forming the phase change material 102 on thedielectric material 104 may be increased because the substrate 101 uponwhich the two portions of the phase change material 102 are formed doesnot need to be transferred between tools.

The two portions of the phase change material 102 may also be formedusing a conventional nitrogen or oxygen ion implantation. The phasechange material 102 may be formed by PVD or CVD. Nitrogen or oxygen maythen be implanted into a portion of the phase change material 102,producing the high adhesion phase change material 108 and low adhesionphase change material 110. Alternatively, a thin layer of the lowadhesion phase change material 110 may be formed on the dielectricmaterial 104 by PVD. The substrate 101 may then be removed from thedeposition chamber 134 and the low adhesion phase change material 110may be implanted with nitrogen or oxygen ions to form the high adhesionphase change material 108. The substrate 101 may then be placed backinto the deposition chamber 134 to form the low adhesion phase changematerial 110 by PVD over the high adhesion phase change material 108.Utilizing ion implantation may provide improved control of thedistribution of the nitrogen or oxygen atoms throughout the phase changematerial 102. By way of non-limiting example, a high atomic percentageof nitrogen or oxygen may be achieved at the interface between thedielectric material 104 and the high adhesion phase change material 108,providing increased adhesion between the dielectric material 104 and thephase change material 102.

The phase change material 102 on the dielectric material 104 may beformed in an amorphous state or in a crystalline state by adjusting thechuck temperature. If the chuck temperature is maintained atapproximately room temperature during the deposition of the phase changematerial 102, the phase change material 102 may be deposited in anamorphous state. At a deposition temperature above room temperature, thephase change material 102 may be deposited in a crystalline state. Byway of non-limiting example, the phase change material 102 is depositedin a crystalline state. Alternatively, a portion of the phase changematerial 102 may be deposited in the amorphous state and another portionof the phase change material 102 may be deposited in the crystallinestate.

If the phase change material 102 is a GST material, the GST material maybe deposited in a crystalline state by maintaining the temperature inthe deposition chamber 134 at above room temperature. In one embodiment,the as-deposited phase change material 102 is a crystalline GST materialsince the resistance of the crystalline GST material is on the order ofkiloOhms (kΩ), while the resistance of the amorphous GST material is onthe order of megaohms (MΩ).

The following examples serve to explain embodiments of the presentinvention in more detail. These examples are not to be construed asbeing exhaustive or exclusive as to the scope of this invention.

EXAMPLES Example 1

A GST material was deposited by PVD on a silicon nitride substrate. TheGST material was deposited by PVD using a Ge₂Sb₂Te₅ deposition targetand an argon plasma generated in an Entron EX300 RF sputtering chamber.During the deposition, the PVD chamber was maintained at 6.6 mTorr andat room temperature, and 1 KW RF power was applied to the Ge₂Sb₂Te₅deposition target for 66.1 seconds. The argon flow rate was 200 sccm andthe nitrogen flow rate was 5 sccm during the deposition. The resultingGST material had a thickness of 1000 Å and included 7.0% (atomic) ±1.5%(atomic) nitrogen.

The GST-covered silicon nitride substrate was then subjected to a fourpoint bend test to measure the fracture energy sufficient to causeadhesion failure between the GST material and the silicon nitridesubstrate. The GST-covered silicon nitride substrate was positionedbetween two silicon wafers and bonded face to face using an epoxy. Twoforces were applied to a top surface of the sandwiched structure, nearouter portions of the sandwiched structure, while two forces wereapplied to an inner portion of the opposing surface of the sandwichedstructure. The fracture energy was measured as the energy per unit arearequired to separate the GST material from the silicon nitridesubstrate. As the bending moment increased, a pre-crack initiated fromthe top surface (facilitated by a machined notch) and propagatedvertically to the interface. The debond strain energy release rate,G_(c), was calculated by the following equation:

$G_{c} = \frac{21\left( {1 - r^{2}} \right)P_{c}^{2}L^{2}}{16{Eb}^{2}h^{3}}$

where v is Poission's ratio for the substrate, L is the distance betweenthe inner and outer forces, E is the Young's modulus of the substrate, bis the width of the sandwiched structure, h is one half of the thicknessof the sandwiched structure, and P_(c) is the plateau load (criticalload). P_(c) is determined by graphing the load, P, versus thedisplacement. P_(c) corresponds to the horizontal plateau in theload-displacement curve during the four point bend test. The P_(c) isthe load at which the load plateaus while the displacement continues toincrease. The fracture energy for the GST-covered silicon nitridesubstrate was 1.52 J/m²±0.12 J/m².

For comparative purposes, a GST material was deposited as describedabove except the nitrogen flow rate was maintained at 1 sccm during thedeposition. The resulting GST-covered silicon nitride substrate materialincluded 2.5% (atomic)±1.5% (atomic) nitrogen. The fracture energy forthis GST-covered silicon nitride substrate was 0.74 J/m²±0.08 J/m².Since the GST-covered silicon nitride substrate formed at a nitrogenflow rate of 5 sccm had a higher nitrogen content and fracture energythan the GST-covered silicon nitride substrate formed at a nitrogen flowrate of 1 sccm, the former exhibited improved adhesion to siliconnitride.

Example 2

A first portion of a GST material was formed on a silicon nitridesubstrate by PVD. The GST material was deposited by PVD using aGe₂Sb₂Te₅ deposition target and an argon plasma generated in an EntronEX300 RF sputtering chamber. During the deposition, the PVD chamber wasmaintained at 6.6 mTorr and at room temperature, and 1 KW RF power wasapplied to the Ge₂Sb₂Te₅ deposition target for 66.1 seconds. The argonflow rate was 200 sccm and the nitrogen flow rate was 5 sccm during thedeposition. The nitrogen flow rate was maintained at 5 sccm until thefirst portion of the GST material was 50 Å thick. Then, the nitrogenflow rate was decreased to 1 sccm to form the second portion of the GSTmaterial. The deposition of the second portion was conducted until thetotal thickness of the GST material was 1000 Å. The resultingGST-covered silicon nitride substrate included about 50 Å of a GSTmaterial including 7.0% (atomic)±1.5% (atomic) of nitrogen, and about950 Å of a GST material including 2.5% (atomic)±1.5% (atomic) ofnitrogen. The fracture energy for the GST material and the siliconnitrate substrate was 0.94 J/m²±0.08 J/m².

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the inventionencompasses all modifications, variations and alternatives fallingwithin the scope of the invention as defined by the following appendedclaims and their legal equivalents.

1. A phase change material, comprising: at least two portions of achalcogenide compound material, a first portion of the chalcogenidecompound material comprising a greater amount of at least one ofnitrogen and oxygen than a second portion.
 2. The phase change materialof claim 1, wherein the chalcogenide compound material comprises achalcogen ion selected from the group consisting of oxygen, sulfur,selenium, tellurium, and polonium and at least one electropositiveelement selected from the group consisting of nitrogen, silicon, nickel,gallium, germanium, arsenic, silver, indium, tin, antimony, gold, lead,and bismuth.
 3. The phase change material of claim 1, wherein thechalcogenide compound material comprises an empirical formula ofGe_(x)Sb_(100-(x+y))Te_(y), wherein x ranges from approximately 5 atomicpercent to approximately 60 atomic percent and y ranges fromapproximately 20 atomic percent to approximately 70 atomic percent. 4.The phase change material of claim 1, wherein the first portion of thechalcogenide compound material comprises greater than or equal to about5 atomic percent of at least one of nitrogen and oxygen.
 5. The phasechange material of claim 1, wherein the first portion of thechalcogenide compound material comprises from greater than or equal toabout 5 atomic percent of at least one of nitrogen and oxygen to lessthan or equal to about 8 atomic percent of at least one of nitrogen andoxygen.
 6. The phase change material of claim 1, wherein the secondportion of the chalcogenide compound material comprises less than about4 atomic percent of at least one of nitrogen and oxygen.
 7. The phasechange material of claim 1, wherein the second portion of thechalcogenide compound material comprises approximately 2.5 atomicpercent of at least one of nitrogen and oxygen.
 8. The phase changematerial of claim 1, wherein the first portion of the chalcogenidecompound material and the second portion of the chalcogenide compoundmaterial comprise a substantially heterogeneous phase change material.9. The phase change material of claim 1, wherein the first portioncomprises a thickness of from approximately 10 angstroms toapproximately 100 angstroms.
 10. A phase change random access memorydevice, comprising: an electrode within a dielectric material, a phasechange material in contact with the electrode and the dielectricmaterial, and another electrode in contact with the phase changematerial, wherein the phase change material comprises at least twoportions, at least one of the at least two portions comprising adifferent nitrogen or oxygen content than the other of the at least twoportions of the phase change material.
 11. The phase change randomaccess memory device of claim 10, wherein the portion of the phasechange material in direct contact with the dielectric material comprisesa greater amount of nitrogen or oxygen than other portions of the phasechange material.
 12. The phase change random access memory device ofclaim 10, wherein a fracture energy between the phase change materialand the dielectric material is at least about 0.94 J/m².
 13. The phasechange random access memory device of claim 10, wherein a fractureenergy between the phase change material and the dielectric material isat least about 1.5 J/m².
 14. The phase change random access memorydevice of claim 10, wherein a fracture energy between the phase changematerial and the dielectric material is at least about 2.0 J/².
 15. Asemiconductor structure, comprising: a phase change material formed on adielectric material, the phase change material comprising at least twoportions, wherein one of the two portions directly contacts thedielectric material and comprises a higher percentage of at least one ofnitrogen and oxygen than the other of the at least two portions of thephase change material.
 16. A method of forming a phase change material,comprising: forming a chalcogenide compound material on a substrate, thechalcogenide compound material comprising a first portion comprising apercentage of at least one of nitrogen and oxygen and a second portioncomprising a lower percentage of at least one of nitrogen and oxygenthan the first portion.
 17. The method of claim 16, wherein forming achalcogenide compound material on a substrate comprises depositing thechalcogenide compound material by physical vapor deposition.
 18. Themethod of claim 16, wherein forming a chalcogenide compound material ona substrate by physical vapor deposition comprises depositing thechalcogenide compound material in the presence of at least one ofnitrogen gas and oxygen gas.
 19. The method of claim 16, wherein forminga chalcogenide compound material on a substrate comprises implanting atleast one of nitrogen and oxygen into a portion of the chalcogenidecompound material.
 20. A method of forming a phase change material,comprising: positioning a substrate comprising a dielectric material ina deposition chamber; generating a plasma in the deposition chamber;introducing at least one of nitrogen gas and oxygen gas into thedeposition chamber; forming a first phase change material on thedielectric material, the first phase change material comprising anamount of at least one of nitrogen and oxygen; and forming a secondphase change material on the first phase change material, the secondphase change material comprising a lower amount of at least one ofnitrogen and oxygen than the first phase change material.
 21. The methodof claim 20, wherein introducing at least one of nitrogen gas and oxygengas into the deposition chamber comprises introducing the at least oneof nitrogen gas and oxygen gas into the deposition chamber at a flowrate of from 0 sccm to at least 5 sccm.
 22. The method of claim 20,wherein forming a first phase change material on the dielectric materialcomprises introducing from greater than about 1 sccm to about 5 sccm ofthe at least one of nitrogen gas and oxygen gas into the depositionchamber.
 23. The method of claim 20, wherein forming a second phasechange material on the first phase change material comprises introducingat least one of nitrogen gas and oxygen gas into the deposition chamberat a flow rate of less than about 1 sccm.
 24. The method of claim 20,wherein forming a first phase change material comprises forming a phasechange material comprising greater than or equal to about 5 atomicpercent of at least one of nitrogen and oxygen.
 25. The method of claim20, wherein forming a second phase change material comprises forming aphase change material comprising less than about 4 atomic percent of atleast one of nitrogen and oxygen.